riscv: Improve sbi_ecall() code generation by reordering arguments

riscv: Improve sbi_ecall() code generation by reordering arguments

The sbi_ecall() function arguments are not in the same order as the
ecall arguments, so we end up re-ordering the registers before the
ecall which is useless and costly.

So simply reorder the arguments in the same way as expected by ecall.
Instead of reordering directly the arguments of sbi_ecall(), use a proxy
macro since the current ordering is more natural.

Before:

Dump of assembler code for function sbi_ecall:
   0xffffffff800085e0 <+0>: add sp,sp,-32
   0xffffffff800085e2 <+2>: sd s0,24(sp)
   0xffffffff800085e4 <+4>: mv t1,a0
   0xffffffff800085e6 <+6>: add s0,sp,32
   0xffffffff800085e8 <+8>: mv t3,a1
   0xffffffff800085ea <+10>: mv a0,a2
   0xffffffff800085ec <+12>: mv a1,a3
   0xffffffff800085ee <+14>: mv a2,a4
   0xffffffff800085f0 <+16>: mv a3,a5
   0xffffffff800085f2 <+18>: mv a4,a6
   0xffffffff800085f4 <+20>: mv a5,a7
   0xffffffff800085f6 <+22>: mv a6,t3
   0xffffffff800085f8 <+24>: mv a7,t1
   0xffffffff800085fa <+26>: ecall
   0xffffffff800085fe <+30>: ld s0,24(sp)
   0xffffffff80008600 <+32>: add sp,sp,32
   0xffffffff80008602 <+34>: ret

After:

Dump of assembler code for function __sbi_ecall:
   0xffffffff8000b6b2 <+0>:	add	sp,sp,-32
   0xffffffff8000b6b4 <+2>:	sd	s0,24(sp)
   0xffffffff8000b6b6 <+4>:	add	s0,sp,32
   0xffffffff8000b6b8 <+6>:	ecall
   0xffffffff8000b6bc <+10>:	ld	s0,24(sp)
   0xffffffff8000b6be <+12>:	add	sp,sp,32
   0xffffffff8000b6c0 <+14>:	ret

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Yunhui Cui <cuiyunhui@bytedance.com>
Link: https://lore.kernel.org/r/20240322112629.68170-1-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>